1. Field of the Invention
This invention relates to sealing systems for air heaters and more particularly to a sealing system with a deformable sector plate for effecting seals between the portions of an air heater which move relative to each other.
2. Discussion of the Related Art
It is typical in fuel burning installations or devices, such as electrical power generating plants, to use regenerative air preheaters for heating the intake air to improve the efficiency of the fuel burning operation. These air preheaters typically include two major components, namely, a generally cylindrical drum having a matrix of heat exchanging elements therein and a surrounding housing having a generally cylindrical opening therein. One type of preheater has a stationary drum and a movable housing surrounding the drum. This type of air preheater is known as a Rothermuhle type air preheater, which is exemplified in U.S. Pat. No. 3,802,489 assigned to Apparatebau Rothermuhle Brandt & Kristzler of Wenden, West Germany, which patent is incorporated herein by reference. However, the most commonly used preheaters are those of the Ljungstrom type in which the drum is a cylindrical rotor containing metallic heat transfer plates, the rotor being movable with respect to a surrounding stationary housing. As the rotor turns, the heat transfer plates are first exposed to hot discharge gases, and these heated plates then move into the air intake passage to heat the incoming air. The housing surrounding the drum includes sector plates which divide the housing into an air intake half and gas discharge half. In an attempt to reduce the mingling of the two fluids, the drum is typically provided with radially extending seal plates that are intended to pass closely by the sector plates with only a small clearance.
A major problem with the foregoing sealing arrangement is that it depends on achieving small, constant and predictable clearances between the seal plates and adjacent surfaces. Such clearances are difficult to attain even in a newly manufactured air preheater, and are particularly difficult to maintain in an air preheater that is in service. Air preheaters, when in service, are subject to extremes in temperature and a very hostile environment. Factors such as wear, distortion of parts due to temperature differentials, normal dimensional changes due to heating and cooling, lack of flatness in the sector plates, out of roundness of the drum and/or adjacent housing portion, and various other factors contribute, in practice, to wide variation in the clearances between moving parts. One particular problem is that the drum and its seal plate tend to assume a bowed shape when heated, the hotter end of the drum assuming a convex shape and the less hot end a concave shape. Excessive clearances of threequarters of an inch have been known as well as a complete lack of clearance in which there is an unintentional clashing of the metal seal plates with the adjacent sealing surfaces. These problems are further aggravated by the hostile environment to which an air preheater is subjected. The dirty, soot and acid-laden discharge gas which passes through the air preheater results in soot buildup, corrosion, and wear, all of which contribute to irregularities in the relatively movable parts. The irregularities, of course, lead to sealing difficulties.
Attempts to maintain a constant clearance between the sector plates and adjacent radial seals have only been partially successful. For example, U.S. Pat. No. 4,124,063 discloses sector plates which are deflected at their outer ends by a mechanical actuator. This mechanical actuator is responsive to axial movements of the axle. Accordingly, as the axle is thermally deformed, the sector plate is forced into a dish configuration to minimize leakage between it and the deformed radial seals. However, the mechanical actuator will eventually break down as a result of the intense conditions discussed above, causing the sector plate to contact the radial seals and leading to a shut-down of the air preheater for time consuming repair. More significantly, this deflection of the sector plate ends results in a clearance which does not conform to the spherical deformation experienced in the radial seals as they are heated. Accordingly, leakage occurs between the sector plates and the radial seals.
Another currently used sealing system is shown in U.S. Pat. No. 4,122,891 and uses a hinged sector plate. Each hinged portion is independently actuated in response to the thermal expansion of the axle. In addition to the longevity and maintenance problems discussed above, this system does not result in optimum leakage control since the sector plate portions at best can only maintain a tangential relationship with the spherically deformed radial seals, resulting in leakage.
Another sealing system is shown in U.S. Pat. No. 4,024,907. This system uses a screw jack to deform the outer portion of the sector plate in an attempt to conform to the spherical deformation of the radial seals. However, such deformation results in the sector plate being tangential to the spherically curved radial seals, resulting in leakage between the two halves of the drum.
In presently known air preheaters, particularly those of the Ljungstrom type, additional sealing problems are encountered at the circumference of the drum where the radial seals end. Such sealing problems are also encountered adjacent the drum axle, near where the radial seals begin. At present, it is typical to provide post seals adjacent the drum axle and circumferential seals adjacent the drum periphery. The radial seals then extend between the post and circumferential seals. Such a sealing arrangement, however, creates gaps between the different types of seals, which gaps contribute to an undesirable amount of leakage along paths which bypass the heat exchanging drum of the air preheater Heretofore, it has not been known how to eliminate these gaps in a Ljungstrom type air preheater.
It is an object of the present invention to maintain a constant clearance between the radial seals and the sector plates of an air preheater throughout the wide range of operating temperatures of air preheaters.
It is a further object of the present invention to maintain such a constant clearance simply without the use of complicated actuators.
It is yet another object of the present invention to provide a continuous: perimeter seal for an air preheater, i.e., it is an object of the invention to seal an air preheater such that there are no discontinuities in the seal perimeter.
More specifically, it is an object of the present invention to improve the total sealing package for an air preheater by providing unbroken seals completely around the paths through which flue gases flow from the furnace and intake air flows toward the furnace, such unbroken seals being located in the areas between the drum and housing.
It is a further object of the present invention to provide an air preheater in which such continuous, unbroken seals take the form of flexible expansion joints.
It is a related object of the present invention to replace the presently known arrangement of post seals, radial seals and circumferential seals, which known seals result in gaps which create leak paths, with gapless flow paths for the intake air and the flue gases.
It is a further object of the present invention to provide such gapless flow paths in a Ljungstrom type air preheater.
Other objects and advantages of the present invention will become apparent in the specification and drawings which follow.